Study of Noises in Partial Discharge Measurement on Power Cables

Methods of noise reduction were studied for partial discharge location on 77kV XLPE power cables in consideration that noises are a major problem in partial discharge measurement. A noise survey was conducted at first in the field. Noise spectra showed high peaks at frequencies over 200kHz and 550kHz possibly of radio wave origin. A study on the points of noise penetration indicated that a large part of noises is induced in cable conductor by noise current flowing in the outer shielding layer. The use of band elimination filters was tested, as a method of noise elimination, to cut high frequencies. The method tested in the filed was effective on steady noises and reduced the noise level to about one-twentieth under optimal conditions.